The invention relates to a method and a device for coating a continuously delivered sheet formation, with the features of the preamble of the independent patent claims.
In coating technology it is known to manufacture interlinings with the so-called double-point method. The combination of two known coating methods (paste-point coating and scatter coating) permits the unification of the properties of various types of melting adhesive at one point which consists of the so-called lower point and of the upper point. A mostly thermoplastic material is deposited onto the sheet formation to be coated (typically a textile material web) at individual points (paste sections). Subsequently for forming the upper point a low melting plastic is scattered on. The low melting plastic forming the upper point sticks to the moist, sticky surface of the lower point. On the remaining surface of the sheet formation the plastic lies loosely. In a next method step the powder-like and low-melting adhesive which is scattered on is sucked off. Only on the lower points does the powder-like adhesive remain sticking and thus forms an exactly placed upper point.
In a subsequent method step the material web coated in this way undergoes a thermal treatment method and the powder layer which is scattered on is melted on and fixed.
With this double-point coating method there occurs various problems. As such it is particularly difficult to completely remove the powder-like layer which is scattered on in the regions outside the lower points. If there is still powder present between the individual lower points, then this is likewise fixed onto the sheet formation in the subsequent thermal treatment.
With known methods the sheet formations are hit/beaten in order to loosen the powder. Thereafter by way of suction means it is removed from the surface of the sheet formation. This method however is flawed with the disadvantage that due to the acceleration on beating, the powder penetrates the sheet formation. It may then only be sucked out of the sheet formation incompletely and with difficulty.
It is further also known to blow through the textile web with an air jet and to simultaneously suck of the particles on the opposite side. So that the textile web does not flutter or lift off during the blowing, it must however be held by suction means from below. By way of this, likewise a part of the powder is suctioned into the web and here sets firmly. Moreover this method is not applicable to all sheet formations since the effectiveness depends on the porosity of the material of the sheet formation. Dense material is difficult to blow through from below.
It is the object of the invention to avoid the disadvantages of that which is known, in particular to provide a method and a device for coating a sheet formation with a double-point layer which permits a reliable removal of the powder layer which is scattered on. The method and the device are also to be able to be simply carried out so that no additional measures for fixing the material web are necessary.
According to the invention these objects are achieved with a method and a device with the features of the characterising part of the independent patent claims.
With a method for coating a continuously supplied web-like sheet formation, in a first method step a paste-like plastic layer is deposited in sections distanced to one another, preferably in point-shaped sections. In a subsequent method step a second layer of a powder-like, thermoplastic plastic with a preferably lower melting temperature is scattered onto the first paste-like layer. This two-point coating subsequently undergoes a thermal treatment.
Before the thermal treatment, the powder deposited between the sections of the first plastic layer is swirled up by an air jet directed obliquely against the surface of the sheet formation. Simultaneously the powder particles which are swirled up are sucked off in a directed manner directly over the material web by way of a suction means. The air jet directed obliquely towards the surface of the sheet formation does away with the need for holding devices for the material web before the sucking off. The attack direction of the air jet and the turbulences in the region of the surface of the material web lead to an optimal release of the powder particles from the surface of the sheet formation.
In a particularly advantageous embodiment the air jet is directed at an angle of 80xc2x0 to 30xc2x0 to the surface of the sheet formation against this surface. The angle is preferably 75xc2x0 to 60xc2x0.
In a further advantageous embodiment the air jet is directed towards the running direction of the sheet formation.
In a further preferred embodiment the material web in the region of the impinging air jet is led over an impact plate. This is particularly advantageous with sheet formations which are less dense. The impact plate on the one hand serves as a resting surface for the blow means and permits a quiet transport of the material. On the other hand in the start and deflection region of the air jet there forms turbulences, even with less dense material, which simplifies the releasing of the thermoplastic powder from the material web.
It has further been shown that it may be advantageous to submit the powder which is scattered on advantageously to an ionisation treatment. If the air jet is led through a heavy, electrical alternating field before impinging on the surface of the sheet formation, the static charge of the powder particles may be heavily reduced. With this, on the one hand the direct influence of the alternating field on the powder particles, and on the other hand the ionised air jet play their part. The arrangement of an alternating field reliably helps the removal of a static charge of the powder particles. The combination of the suctioning and blowing-on furthermore leads to an advantageous holding-down effect. The forces of the two air flows on the material web compensate one another.
The device according to the invention consists essentially of a coating arrangement for depositing the first paste-like layer and of a scattering arrangement for scattering on the second powder-like layer.
The device is moreover provided with a transport arrangement for conveying the sheet formation from the coating arrangement to the treatment arrangement connected thereafter.
Between the scattering arrangement for depositing the powder and the treatment arrangement connected thereafter there is provided a means for removing the powder deposited between the sections of the first layer. The means consist of a blow means for blowing an air jet directed obliquely to the surface of the sheet formation, and a suction means for sucking off the powder swirled up by the air jet.
Advantageously the blow means is arranged such that the blow jet impinges the surface of the sheet formation at an angle of 80xc2x0 to 30xc2x0, preferably at 75xc2x0 to 60xc2x0.
In a further preferred embodiment example the device according to the invention is further provided with an impact plate via which the sheet formation can be guided in the region of the blow means and of the suction means.
Furthermore the device is preferably provided with an ionisation arrangement for ionising the blow air and for producing an electrical alternating filed.